Telecommunication networks for mobile devices include cellular communication systems; mobile Internet Protocol (IP) networks; paging systems; and others. Cellular systems generally allow mobile terminals to move geographically by “handing off” localized communication links among transmission towers and associated base stations. Similarly, mobile IP networks allow IP-enabled devices such as wireless Personal Digital Assistants (PDAs) and mobile computers to move about geographically dispersed areas while maintaining a connection to the Internet.
Mobile devices can provide both voice-based connections and IP connections using different base stations and infrastructures. For example, a Web-enabled cell phone might maintain a voice connection using a first transmission channel and maintain a mobile IP connection using a second (and independent) transmission channel, such that handoffs occur independently for the two channels. Alternatively, voice services can be combined with the IP service, such that a single connection is maintained for both services. Voice connections can also be provided over IP in a combined service.
FIG. 1 shows a conventional mobile IP network that covers three service areas SA1, SA2, and SA3. For the sake of simplicity, only IP services are shown, although as explained above, separate transmission networks can be provided for voice services.
As shown in FIG. 1, a mobile terminal MT is within service area SA1 served by base station BS1 (also called an access point or AP). Base station BS1 is connected to an access router AR1, which in turn connects to an Internet service provider ISP1 that provides access to the Internet. Other base stations such as BS3 may also be connected to access router AR1, such that a common IP address is used for mobile terminals even though the terminals may pass through different service areas. In other words, although there may be a hand off of radio frequency channels when the mobile terminal moves between service area SA1 and service area SA3, it may not be necessary to change the IP address used to communicate with the mobile terminal because the Internet connection is still served by the same access router AR1.
A second service area SA2 is served by a separate base station BS2, which is in turn connected to a different access router AR2. Due to the network topology, access routers AR1 and AR2 use different blocks of IP addresses for communicating with mobile terminals roaming within their associated service areas. If mobile terminal MT moves from service area SA1 to service area SA2, some mechanism is needed to hand off the Internet connection from access router AR1 to access router AR2. Similarly, if service areas SA1 and SA2 are separated by a large logical distance (e.g., AR1 and AR2 are connected to different ISPs), some coordination mechanism is needed to permit data transmitted to a terminal previously operating in service area SA1 to be forwarded to service area SA2 if that terminal moves into area SA2.
One conventional scheme for handing off IP connections is depicted in FIG. 2. Service area SA1 is served by access router AR1, which is designated the “home agent” for communicating with a particular mobile terminal MT. While mobile terminal MT moves within service area SA1, access router AR1 communicates with the mobile terminal using an IP address that is assigned to access router AR1. IP packets (e.g., e-mail, Web pages, and the like) are transmitted over the Internet to ISP1, which forwards the traffic to AR1, which in turn knows that a particular IP connection is associated with the mobile terminal in its service area.
If mobile terminal MT moves to a different service area SA2 served by a different access router AR2, packets that were previously transmitted to AR1 will no longer reach the mobile terminal. One conventional solution is to advertise (e.g., broadcast) the existence of access router AR2 in service area SA2, such that when mobile terminal MT moves into service area SA2, it is notified of the existence of access router AR2, and it receives a new IP address for communicating within service area SA2. Mobile terminal MT or access router AR2 then sends a binding update to home agent AR1 (e.g., through a land line LL or over the Internet), so that home agent AR1 knows the IP address that will allow packets to reach the mobile terminal in service area SA2. The home agent treats this address as a “care of” address, and all further packets to the original IP address are forwarded to the new IP address. In essence, two separate IP addresses are used to communicate with the mobile terminal: a home agent address and a care of address that changes at each new point of attachment. This scheme is described in the Internet Engineering Task Force (IETF) Request for Comments (RFC) number 2002 (October 1996).
The above scheme assumes that the target access router (AR2) is known by the originating access router (AR1) prior to the handoff (e.g., mobile terminal MT has accepted the advertisement from AR2 and is assigned an IP address for communicating with it). If there are multiple access routers in the target area each with overlapping service areas, there is no easy way for the mobile terminal to select from among them. For example, suppose that a mobile terminal is receiving high bandwidth video data while moving out of a service area. Two other overlapping service areas served by two access routers controlled by two different service providers may be available to accept the handoff of the mobile terminal's IP connection. One of the two access routers may provide high-speed access to the Internet, while the second one may not. There is no way for the mobile terminal to specify or select from among the two access routers.
Another problem concerns handoff speed. The conventional scenario shown in FIG. 2 may not be able to provide fast handoff speed because of the handshaking required between the mobile terminal and the new access router AR2. Packets may be lost if handoff of the IP connection is not performed smoothly. Moreover, if an IP connection is used for voice-quality signals or music, latency introduced by the handoff may unacceptably disrupt the connection.
Another difficulty with handing off IP connections in mobile networks arises where heterogeneous networks (using different access technologies) served by potentially different (and incompatible) service providers are concerned. Referring again to FIG. 1, if service area SA1 is served by MCI while service area SA2 is served by AT&T, then the two service providers must agree on a coordination mechanism to accept handoffs of IP services from each other's system. Moreover, as new access routers are added to each service provider's system, the details of each new access router must be communicated throughout the system (e.g., from a central authority) to ensure that all access routers in both systems are aware of the others. This approach can result in a single point of failure, and requires coordination of effort among different service providers.
The problem of providing seamless handovers in IP environments is related to ongoing efforts in the Internet Engineering Task Force (IETF), namely in the Context Transfer, Handoff Candidate Discovery, and Seamless Mobility (SeaMoby) and Mobile IP working groups. Context transfer and fast handover protocols have been developed to exchange session-related information or proactively establish mobile IP connectivity, respectively. Both protocols assume that the target access router is known when requesting the desired functionality (see FIG. 1). Although the discovery of the handoff candidate is included in the SeaMoby working group charter, discovery protocols for physically adjacent access routers have not been studied so far. However, research regarding obtaining physical locations of networking elements has been conducted. Location tracking technologies, such as the Global Positioning System (GPS), provide physical location information of devices attached to the positioning system. Other systems use such information to accurately locate devices. However, since the location is not in relation to any coverage area of an access technology, the location information is not applicable for candidate selection purposes.
Location systems based on radio frequency technologies use the signal of the wireless access technology to determine the position of the mobile node. In contrast to GPS systems, the obtained location is related to the coverage area of the base station being used for location determination. However, the obtained location is specific for the mobile node and does not give any indication of overlapping coverage areas of access routers. Thus, these systems cannot be used to determine physically adjacent networking elements. Moreover, the location determination is usually very specific for the access technology used, and is therefore not suited for multiple access technology scenarios. Besides the lack of accuracy of the obtained location, there is no indication of overlapping coverage areas needed for physical adjacency determination.
What is needed is a system and method for addressing some or all of the aforementioned problems.